Transition from Wigner crystal to Wigner molecule
Picture shows snapshots of the arrangement of N=19 electrons at low temperature
when the density (confinement strength) is increased, giving rise to
increasing overlap of the neighboring electron clouds.
Notice the regular symmetry of this cluster: with 1, 6 and 12 electrons on the
three shells each electron is part of an almost perfect triangular lattice cell.
This cluster is, therefore, called "magic", it has unusually high stability against
inter-shell rotation, see the figure below.